Skin care and pharmaceutical compositions containing dissolved gases, such as oxygen and carbon dioxide, apart from ordinary propellants, have become the focus of great interest in recent years. For example, it has been suggested that topically applied oxygen-containing formulations may induce the growth of blood vessels and new skin, improve skin metabolism, impede skin aging, and protect skin from injurious environmental effects (Oxynoid, O. E. et al., Art. Cells, Blood Subs., and Immob. Biotech., 1994, 22(4), 1331–1336). Similarly, topically applied carbon dioxide-containing cosmetic compositions are claimed to stimulate blood circulation, improve dull looking skin, and diminish dark circles under eyes and uneven skin tone (U.S. Pat. No. 6,228,378). Accordingly, a number of topical cosmetic and therapeutic compositions containing dissolved gases, in particular oxygen and carbon dioxide, have been developed.
For example, U.S. Pat. No. 4,366,169 describes the use of oxygen-containing fluorocarbons (FCs) in the treatment of ischemic wounds such as those resulting from burns, cuts, abrasions, and surgeries (U.S. Pat. No. 4,366,169). U.S. Pat. No. 5,885,564 teaches oxygen-containing FC emulsions that include digestive treatment products of cells of vegetable matter or yeasts. It is believed that the synergy between FCs and digestive treatments lead to a higher oxygen content in the emulsion. U.S. Pat. No. 6,228,378 describes a viscous cosmetic composition containing carbon dioxide gas.
Gas-containing products are typically hermetically packaged in pressurized containers to avoid the loss of the contained gas to the outside. Dispensing systems which use pressurized containers are well known. In such systems, the product to be dispensed is provided in the container and the container is charged to a starting pressure. When the dispensing valve is activated, a pressure differential between the internal pressure of the dispenser and the ambient pressure results in the dispensing of the product from the container (U.S. Pat. No. Re.35,540). However, as the product is dispensed from a conventional pressurized container, displaced liquid volume within the container is filled with expanding gas and the container pressure decreases proportionately in accordance with Boyle's Law. As a result, concentration of the gas in the product decreases in proportion to the overall pressure loss within the product container. Therefore, conventional pressurized containers fail to maintain gas concentration in the product that is subject to recurring dispensing. Because most conventional pressurized, or aerosol cans only use dissolved volatile gas as a propellant for product delivery, and not for therapeutic purposes, this limitation is generally not problematic. However, the maintenance of high pressure within the product container during dispensation would advantageously ensure a high level of dissolved gas in the product throughout its use.
Recently, U.S. Pat. No. 6,228,378 suggested packaging a composition containing carbon dioxide into a container of a dual structure comprising an outer container and an inner bag. In order to achieve a high concentration of the carbon dioxide gas in the cosmetic composition, the inner bag is made of a gas permeable material and carbon dioxide gas is used as a propellant. The patent teaches “aging” the cosmetic composition for one week at room temperature to allow the carbon dioxide gas to permeate through the inner bag into the cosmetic composition in order to obtain the desirable gas concentration level. The “aging” process can be shortened by heating.
This approach, however, is not practical in cosmetic and therapeutic applications. Typical cosmetic and therapeutic applications require frequent, e.g., daily, dispensing of the product. Accordingly, there would not be sufficient time between the applications to carry out the required “aging.” Also, such a system makes maintaining constant gas concentration in the product difficult, if not impossible. The “aging” process as described appears to be based on simple diffusive transport of carbon dioxide across the permeable membrane. This process is very slow and fails to provide even approximate control over the carbon dioxide levels within the dispensed product. In order to achieve constant gas concentration in the product, a careful metering of the “aging time” and maintaining the product under constant ambient conditions between the applications is required, which is not always practical. Furthermore, because the gas concentration is such a scheme is proportional to the charging gas pressure external to the permeable bag, as product is dispensed both the gas pressure and product gas concentration will decrease.
Therefore, currently available methods for packaging products containing dissolved gases either fail to maintain the gas concentration in the product or suffer from technical disadvantages that make their utilization in cosmetic and therapeutic products impractical.